letter to get shale samples from oil company or institute for research purpose

Actually I am from Pakistan, and I'm studying my master's in Petroleum engineering from China, my research is on shale oil and shale gas, so my professor ( supervisor) told me to bring some shale oil or shale gas samples from Pakistan for research purpose, he told me to talk to some oil company or institute , that we can collaborate with them , we will do research on their samples and then we can give them the results. so I need a letter for that, the letter should be from my professor side